1. Field of the Invention
The present invention relates to an exposure apparatus and a device fabrication method.
2. Description of the Related Art
The performance of an exposure apparatus for use in a semiconductor device fabrication process is mainly evaluated based on three points: resolution, overlay accuracy, and throughput. Note that the resolution means the minimum feature size of a pattern that can be precisely transferred, the overlay accuracy means the accuracy of overlaying several patterns, and the throughput is the production capacity (the number of processed wafers) per unit time. Among these three points, several techniques for improving the throughput have conventionally been examined. Examples of these techniques are to increase the exposure energy per unit time, to shorten the time taken for a wafer stage to move between shots, and to shorten the wafer conveyance time (exchange time) taken for wafer exchange.
To shorten the wafer conveyance time, it is necessary to control the wafer state. The wafer often suffers warping or strain due to the dynamic influence of the shape of the transferred pattern or a coating film on it. Such warping or strain of the wafer generates a chucking error upon chucking and conveying the wafer, leading to a shift or drop of the wafer during its conveyance. Under the circumstance, Japanese Patent Laid-Open No. 2006-269867 proposes a technique to change the control conditions of processes associated with exposure, in accordance with warping or strain of the wafer.
Unfortunately, the conventional techniques do not take account of a method of changing, the control conditions of processes associated with exposure, in accordance with the wafer conveyance direction, so the throughput may decrease if these techniques are exploited without considering this aspect.